The invention relates to a belt drive for auxiliary units of an internal combustion engine with which a friction wheel drive is associated for driving a secondary unit provided separately on the internal combustion engine and whose drive wheel cooperates frictionally with a friction wheel, the friction wheel being arranged for adjustment relative to the drive wheel with regard to frictional contact.
DE 39 34 884 A1 discloses a belt drive, wherein the friction wheel is driven through a belt tightener in the belt drive. The friction wheel thus driven indirectly by the belt is arranged with the belt tightener on a rocking lever, while for uncoupling the clamping roll adjustment from the friction wheel adjustment to the secondary unit's drive wheel, an eccentric device serves, which is adjustable by hand in case of need, independently of the clamping roll adjustment.
Also, unpublished patent application P 102 36 746 discloses a belt drive with a friction wheel arrangement in which a friction wheel frictionally cooperating with the outside of the belt in the wrap-around portion of the belt is also in frictional driving communication with the drive wheel of a separate secondary unit. Information for sustaining a driving, permanent position of engagement of the friction wheel with the drive wheel on the one hand and with the belt on the other cannot be learned from this document.
An object of the invention is to offer a constructionally simple readjusting device for a friction wheel cooperating directly by friction with a belt for driving a separate secondary unit to achieve of a proper permanent engagement position of the friction wheel.
The object is achieved in that the friction wheel also cooperates with the outer side of the belt in the area of its contact with a driving wheel of the internal combustion engine or auxiliary unit, and is held in a permanent position of engagement with driving wheel and belt by a rocking lever journaled at the machine end on a cam arranged for rotary movement, while the cam of the readjusting device, driven in rotation under the effect of a spring bias, acts upon the rocking lever in the tensional or pressing direction with spring bias in the corresponding direction.
With the invention a structurally simple readjustment device is advantageously achieved, whose further advantage is a compact configuration.
An advantageously great readjustment range is achieved if the cam is mounted with an eccentricity directed transversely of the tension or pressure direction of the rocking lever as its starting position.
Also, a compact cam system is advantageously achieved in that the rocking lever is journaled by an eye formed in the end section remote from the friction wheel, which is equipped in a recess coaxial with the cam axis with a biased coil turning spring, while the coil spring fixed at one end on the machine side is disposed for rotating action at the other end on the cam.
Furthermore, for the achievement of a readjustment device that is light and small, it is proposed that the cam formed from a plastic be mounted for rotation on a metal sleeve disposed in a recess and receiving the coil spring, which is disposed nonrotationally through an end section of the rotational helical spring passing through the bottom of the metal sleeve and entering conformingly into a cavity on the machine side, and furthermore is fastened, by a threaded bolt coaxial with the cam axis with the interposition of a fastening cover of the cam device, drivingly against an abutment surface on the machine side, and the cam is disposed on the metal sleeve between abutment surface and the fastening cover with axial clearance.
For an advantageously simple construction of the cam device provision is made according to the invention that the metal sleeve has on the fastening cover a marginal cut-out fitted circumferentially corresponding to the adjustability of the friction wheel for the free passage of an end section of the helical spring directed transversely to the cam axis for rotational engagement with the cam, and that the metal sleeve has an additional marginal cut-out for the engagement of an antirotational projection disposed on the fastening cover.
For an adjusting device of short and light-weight construction, the invention furthermore provides that the cam is in connection with the eye of the rocking arm formed from a plastic, with the interposition of a friction bearing sleeve, which is formed relatively close to the eye, with a fork-like friction wheel pickup, and that the cam device of the short-construction rocking arm is disposed between the secondary unit's drive wheel and the drive wheel partly covered by the drive belt on a knob provided on the front of the internal combustion engine. A space-saving arrangement of the adjusting device is thus also achieved.
Lastly, a proposal of the invention is based on the fact that the friction wheel comprises a spoked wheel body formed from plastic, with a support of a rubber material disposed on the external circumference, the spoked wheel body being supported through an integrated, encapsulated rolling bearing against a bearing pin of the fork of the rocking arm.
The invention is described with the aid of a preferred embodiment represented in the drawings.